/wp-admin/includes/ajax-actions.php file line 3006 is creating divide by zero error

[2linctools]

In the /wp-admin/includes/ajax-actions.php file line 3006 it keeps popping up an error in our php error log that says it is trying to divide by zero. It produces an error over and over again.

PHP Warning: Division by zero in /wp-admin/includes/ajax-actions.php on line 3006

This is line 3006:

$max_pages = ceil( $total_posts / (int) $attachments_query->query['posts_per_page'] );

Here is the whole section:

/**
	 * Filters the arguments passed to WP_Query during an Ajax
	 * call for querying attachments.
	 *
	 * @since 3.7.0
	 *
	 * @see WP_Query::parse_query()
	 *
	 * @param array $query An array of query variables.
	 */
	$query             = apply_filters( 'ajax_query_attachments_args', $query );
	$attachments_query = new WP_Query( $query );

	$posts       = array_map( 'wp_prepare_attachment_for_js', $attachments_query->posts );
	$posts       = array_filter( $posts );
	$total_posts = $attachments_query->found_posts;

	if ( $total_posts < 1 ) {
		// Out-of-bounds, run the query again without LIMIT for total count.
		unset( $query['paged'] );

		$count_query = new WP_Query();
		$count_query->query( $query );
		$total_posts = $count_query->found_posts;
	}

	$max_pages = ceil( $total_posts / (int) $attachments_query->query['posts_per_page'] );

	header( 'X-WP-Total: ' . (int) $total_posts );
	header( 'X-WP-TotalPages: ' . (int) $max_pages );

	wp_send_json_success( $posts );
}

Our php error log looks like this: (truncated a lot)

[23-Jul-2021 18:46:05 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 18:46:14 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 18:46:32 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 18:46:34 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 18:58:34 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 18:58:42 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 19:35:22 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 19:35:58 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006
[23-Jul-2021 19:36:01 UTC] PHP Warning:  Division by zero in  /wp-admin/includes/ajax-actions.php on line 3006

[SergeyBiryukov]

Hi there, welcome to WordPress Trac! Thanks for the report.

Introduced in [51145].

It looks like a plugin or theme changes the posts_per_page value to 0 using the ajax_query_attachments_args filter. By default, it's set to 40 in wp-includes/js/media-models.js​.

We should be able to check the value and set $max_pages to 0 too in that case.

[kapilpaul]

Created patch.

This PR will fix the /wp-admin/includes/ajax-actions.php file line 3006 is creating divide by zero error.

Trac Ticket: https://core.trac.wordpress.org/ticket/53773

[audrasjb]

I tested the proposed patch with changing the posts_per_page value using ajax_query_attachments_args filter and it looks like it solves the issue.
Marking for commit.

[SergeyBiryukov]

In 51485:

Media: Check the posts_per_page value in wp_ajax_query_attachments() before using it as a divisor.

This avoids a "Division by zero" PHP warning if a plugin changes the posts_per_page value to zero.

Follow-up to [51145].

Props 2linctools, kapilpaul, audrasjb.
Fixes #53773.

[SergeyBiryukov]

Reopening for backporting to the 5.8 branch.

[desrosj]

In 51507:

Media: Check the posts_per_page value in wp_ajax_query_attachments() before using it as a divisor.

This avoids a "Division by zero" PHP warning if a plugin changes the posts_per_page value to zero.

Follow-up to [51145].

Props 2linctools, kapilpaul, audrasjb, SergeyBiryukov.
Merges [51485] to the 5.8 branch.
Fixes #53773.